Restrict third-party shell plugin capabilities

Reported-by: Roger Piñol <rogerpicar@gmail.com>

shell/services/AuthServiceStore.js

@@ -0,0 +1,34 @@
+// Intentionally not `.pragma library`: QML JavaScript imports get a private
+// module instance per importing component. shell.qml's instance retains the
+// authentication services; a third-party plugin importing this file receives
+// a separate empty store rather than a shared path to credential-bearing QML.
+
+var services = ({})
+
+function has(id) {
+  return services[String(id || "")] !== undefined
+}
+
+function put(id, service) {
+  var key = String(id || "")
+  if (!key || !service) return
+  if (services[key] && services[key] !== service && typeof services[key].destroy === "function")
+    services[key].destroy()
+  services[key] = service
+}
+
+function ids() {
+  return Object.keys(services)
+}
+
+function destroy(id) {
+  var key = String(id || "")
+  var service = services[key]
+  if (service && typeof service.destroy === "function") service.destroy()
+  delete services[key]
+}
+
+function destroyAll() {
+  var keys = ids()
+  for (var i = 0; i < keys.length; i++) destroy(keys[i])
+}